Imaging sensors frequently encounter low intensity objects where the signal-to-noise ratio is too low for the sensor to obtain sufficient resolution of the object in a single image frame. Accordingly, multiple image frames may be stacked or summed to increase the signal-to-noise ratio and obtain a higher quality image. For example, U.S. Pre-Grant Publication No. 2009/0148065 discloses that CCD (charge-coupled device) cameras, which can be coupled to telescopes for astrophotography, are capable of acquiring multiple images over many seconds and stacking them into a single image. U.S. Pre-Grant Publication No. 2009/0148065 further describes a method whereby images from a plurality of telescopes (or other imaging systems) are combined in real time, effectively constructing image stacks by combining images from a plurality of input sources simultaneously. This method may provide the benefits of a large image stack in a much shorter amount of time than is taken to collect and stack images acquired with a CCD still or video camera mounted on a single telescope.
However, where image frames collected from a single camera over time are stacked, any camera motion between frames blurs the resulting composite image. In addition, independent frame to frame alignment information is required to perform successful frame stacking. For example, inertial sensors (e.g., an inertial measurement unit (IMU)) coupled to the image sensor may provide motion data that can be used to register frames; however, the IMU precision is generally insufficient for accurate frame alignment. Cross-correlation alignment may be used in some circumstances, for example, if the image frames have sufficiently defined points; however, image stacking often may be desired where there are no or an insufficient number of sufficiently defined points available, and poor signal-to-noise ratio in the imaging sensor can prevent cross-correlation adjustment of frames.